Molecular physics: Complexity trapped by simplicity.

Abstract

Devices known as magneto-optical traps have long been used to cool and confine atoms, but not molecules — until now. This new ability should enable many studies and applications of the physics of ultracold molecules. See Letter p.286 In the past decade the use of laser cooling to cool atoms to temperatures close to absolute zero, and their subsequent confinement in magneto-optical traps, has enabled a broad range of applications, from new atomic clocks to novel types of quantum matter. Molecules present a different challenge because the complexity of their internal structure renders current magneto-optical trapping techniques ineffective. Here, Daniel McCarron and colleagues demonstrate the first realization of a magneto-optical trap for a diatomic molecule — they use strontium monofluoride — in a three-dimensional magneto-optical trap. The authors' method is an extension of magneto-optical traps for atoms, but it uses transitions that are rarely exploited for atomic traps. A trapped molecule is an ideal starting point for high-precision measurement of fundamental constants or for the study of chemistry at ultracold temperatures.